There are various systems allowing to know, in real time and from the surface, the pressures, temperatures, flow rates, etc, at a point of a well situated below a test valve while this valve can be open or closed according to the operational phase of the test: flowing or buil-up phase.
Some systems use a hydraulic channel situated in the wall of the test string which communicates the volume under pressure situated below the test valve with pressure gages situated above the valve. The measurements performed by these gages are thereafter transmitted to the surface via an electric cable connected to a sub comprising special electronic means. Connection is achieved by coupling by means of a mutual induction transformer or of a current loop.
Other systems use an acoustic transmission in the body of the test string, for example according to document WO-92/06,278.
The major drawback of the former systems is that they require a test string and more precisely a test valve comprising integration of a hydraulic passage. This assembly type is very complex and very expensive as regards manufacture and maintenance. Besides, in these systems, the electric or mutual inductance connection of the electric cable connecting the measuring means situated above the test valve to the surface is very sensitive to the nature of the fluid present within the production tubing. In particular, transmission is very difficult when the fluids are conductive.
The system illustrated by document WO-92/06,278 also requires an electric type connection between the receiver situated above the valve and the electric cable. Whether a mutual induction connection or a link by means of an electric connector in a liquid environment (wet connector), the drawbacks are the same as with the other known systems.
Furthermore, in these solutions, the transmission distance is limited to practically a pipe length, i.e. about ten meters. Consequently, the connector fastened to the lower end of the electric cable will necessarily be positioned about ten meters above the test valve. If the well produces an effluent containing sand, the latter sediments after closure of the flow rate corresponding to the closure of the test valve, thus forming a plug that can be several ten meters high, which can prevent proper operation of the connector, anchoring or loosening thereof.